I think you would be able if, in addition to what you said above, that:
A) It's a US lens. I'm not sure how Tamron does it but with Nikon it's quite obvious if it is a US lens or not.
B) You send all the paperwork from the US. I'm not sure if the rebate processing people are smart enough to notice a Canadian stamp on the envelope. If they do they may invalid your rebate.
C) The receipt you submit is from a store in the US. Again, it depends on how keen the rebate processing folks are in recognizing a Canadian receipt.