I think the additional waiting would be the issue. It's possible the cab company would agree to take you to the border and leave you in secondary - or if you're let through with minimal delay, they could drop you at bus station or wherever you like across border to get onward taxi/uber/whatever.
I think from secondary examination a Canadian cab could pick you up - not sure, may depend which crossing.
If it's at the crossing in niagara falls which has a footbridge - well, not exactly fun with luggage, but if you can physically manage it, it's not that far.
(I'm not saying which is better, no idea - just might help you avoid waiting fees).