Price Checks for Flights to BUF, YHM, YZZ
    What you see below are very rough estimates, based on price-checks done April 9, 2014.  (but, of course, timings for the cheapest flights might not work well for you)
    You can check the actual prices from your location.

    from USA, generally BUF<YYZ<YHM — I checked low-end prices traveling from three cities (Atlanta, Chicago, San Francisco) to each airport, with round-trip flights on July 24 & 30, for a rough idea of the cost (it seems to be BUF cheapest, then YYZ, then YHM if flights are available) before ground transportation to McMaster.   /   from Atlanta: ATL-BUF (340-380), ATL-YYZ (590,640), ATL-YHM (none).   /   from Chicago: ORD-BUF (230,270,310), ORD-YYZ (345,375), ORD-YHM (none)   /   and from San Francisco: SFO-BUF (470, 565,...), SFO-YYZ (560,620,670), SFO-YHM (780, 960)(740+ on WestJet).

    from Canada, BUF≈YYZ≈YHM:  On the flights I checked, low-end tickets from each airport cost a similar amount. (amounts shown are US Dollars)   But fares may differ from your city, and some airport's options will be better for you in other ways, including the timings and ground-transports.   /   from Vancouver: YVR-YZZ (610-630), YVR-BUF (615), YVR-YHM (620,785) (WestJet, 650+)   /   and from Calgary: YYC-YYZ (580,600), YYC-BUF (590,650), YYC-YHM (580,615 on WestJet).

 
Ground-Transport from BUF to Hamilton/McMaster:

        Wikipedia says that BUF's "proximity... to the 8.4 million residents of Ontario's Golden Horseshoe region makes it a very popular airport for Canadians traveling to U.S. destinations.  In fact, about one of every three passengers utilizing the airport is from Canada." (and more, due to American travelers going to this part of Canada?)   Therefore, I assume there is a good system of ground transport from BUF to Hamilton, which is in the middle of the Golden Horseshoe, although we haven't yet found it.
        A few options for ground transport are described below, but we're hoping to find more-and-better information, to help you find an option that will be convenient (to fit your time schedule), fairly cheap, and fast.   I'm hoping some of you can share "what you know" (or can learn) about this, based on your previous experience or recent research.  If you can help, please contact me: Craig Rusbult, crusbult@wisc.edu.

        Here is what we — Craig Rusbult (writer of the travel page) and Bob Geddes (local chair for the annual meeting) — have discovered so far:
        • Based on the great service of Coach Bus from Madison to Chicago (ORD & MDW) I tried them first, but...  Coach Canada has only one bus per day.  It leaves BUF at 10:45 am, arrives in Hamilton at 2:15 pm (14:15);  return trip begins at 6:15 am in Hamilton, arrives in BUF at 10:00 am.  /  I can't find a fare (the website doesn't seem to allow it) for this trip, but for Hamilton to Niagara Falls it's $21 each way, so maybe it's a little more for a trip to/from BUF?  /  Their homepage does offer trips from BUF to YZZ (thru MegaBus) for $23 or less, 4 times each day, including 4:20-7:20 pm, and then you can go from YZZ to McMaster but that's more ground-traveling than is necessary!
        • Jetways has 4 shuttle buses/day from BUF to Hamilton, for $64 (= $58.34 in US Dollars) or cheaper with groups of 3 ($129 = $118 US = $39/person) which would be a good reason to use ASA's forum for Sharing Airport-Rides.  It goes to/from Hamilton Sheraton Hotel (116 King Street West) and Howard Johnson Hotel (1187 Upper James St) which along with McMaster (1280 Main Street West) you can enter into a trip planner of the local bus system.
        • The website of BUF has a page for Canadian Ground Transportation.  It lists many shuttles/etc, and if you'll be using BUF you can explore the possibilities and (please) report back on what you find.  Thanks.  Craig Rusbult, crusbult@wisc.edu.
 

GO Transit — from Pearson Airport (YYZ in Toronto) to McMaster University
        The travel page describes 3 options for Pearson-to-McMaster including GO Transit.  From the website of GO here is some extra information:
        McMaster U says "GO Transit provides weekday service between Pearson International and campus, with a transfer at the Bramalea GO Station onto the Highway 407 West service."  They don't give details, but here is what I've discovered:
        In the Transit Trip Planner enter "Pearson Airport" and "McMaster University" to get this map for a trip on Bus #107 (or #7) Bus, Hamilton/York University Bus, and #10 Bus.*   ( I'm not sure why this doesn't match the words used by McMaster – "transfer at the Bramalea GO Station onto the Highway 407 West service" – but maybe local people use their own terms that are different than those of GO Transit? ) ( No, this theory isn't correct because when entering another starting time the Trip Planner gives this map which takes you to "Bramalea GO Station" and on to McMaster.  So... I guess there are different ways to achieve the same overall result, and what GO recommends depends on when you begin. )
        WHEN YOU ARRIVE, this map shows how to get from the "GO Bus Terminal" to ASA Registration on Thursday (look at top-center of map) or Friday-Monday (bottom-center of map).
        TIME:  Depending on the time you leave, the trip seems to take about 2 hours.  For comparison, Google Maps says that by driving the trip takes "37 min without traffic," and of course it's longer with traffic.
        COST:  In the fare-calculator for "Select the station..." enter Pearson Airport, then Hamilton & McMaster University, and the single-ride cost is $11.05 for Adult or Student, $5.55 for Senior.
        * By further exploring (with their Trip Planner, try "Route Options" in Google Maps) you might be able to find other options.