I encountered this situation a few times when I was new to Ebay. I simply sent the seller a message explaining my error and apologising for not reading the shipping details more closely.
I also added that I would pay any additional shipping costs associated with shipping to Canada if that would assist them.
In every case, the seller was more than happy to accomodate me and ship the item to me even though it was not their policy to ship to Canada.
If they did not want to ship to me, I felt that at least I had owned up to the error right away, and they could ignore my bid or reject it.
I don't think EBay would take any action give that it was an honest mistake.
Best of luck!