Importing a new car vs servicing a non-domestic car are different issues. Importing a new vehicle means that Tesla would have to make changes to the car to meet Canadian standards. There are about 3-4 items that need to be done. Daytime running lights being the biggest.
This happens whenever there is a big currency discrepancy between Canada and the US. When I bought my S, the cars were cheaper in Canada - especially used ones. As such, several members of the Ontario Club opted to sell their used S models to the US rather than Canada. Up until a couple of years ago, Tesla opted to only allow Roadsters into Canada - now it's all models.
My guess is that Tesla US is protecting it's Canadian operation by saying it won't service a new US car to meet Canadian standards. Tesla has always serviced cars on either side of the border, regardless of its' origin. The OP should not have any issue getting service in Canada.
There are a bunch of threads about this already on this forum. The problem would go away if Tesla would adjust their prices to reflect currency.....but don't hold your breath. Until VW and others start bringing cars into Canada, Tesla has limited competition....so why change