If you decide to cross at Fort Erie/Buffalo, and head down I-90 to I-79, by all means exit I-79 in WV to pick up the "Mountaineer Expressway" (Rt. 19). It will join up with I-77 at the south end, but be aware that there are several towns where the speed limit drops from 65 mph to 50 mph. THESE LIMITS ARE STRICTLY ENFORCED. We always go through at about 47 mph and have never had any issues, but often see some cars pulled over for speeding.
However, seeing that you're from Cobourg, going through the GTA to get to Ft. Erie may not be too appealing! The I-81 route may be preferable for you, but for us being in Oakville, we always cross at the Peace Bridge in Ft. Erie.