I should also probably verify that a ATSC/QAM/NTSC Tuner with CableCARD (TM) Slot tuner means that I can decode HDTV with it from OTA.
ATSC is used for over the air broadcasting of digital signals. None of the Canadian stations listed in TVfool for Callander, ON are actually on the air, or even likely to be on the air anytime in the next few years. It doesn't appear that you have any chance at receiving an American channels where you are.
The QAM tuner might be useful for your local cable company, if they in fact have any unencrypted channels. There is no regulation in Canada requiring Cable Companies to have any unencrypted cable channels, so it may be of limited use.
CableCard is not used in Canada, so CableCard capability is of no use to you.
You can use TVFool to help with aiming for Canadian analog stations in the meantime.
I wouldn't worry too much about overloading your tuner unless you use a preamp, and even then you may be OK. If you do, use one that has separate VHF and UHF inputs, and use separate UHF and VHF antennas. Channels 4 and 6 are pretty powerful in your area.