No threat at all to Boeing from Canada. First of all the 18  'Super Hornets' Canada is going to buy have already been built and are just transfers from the US Navy surplus stock. 
Secondly,  Boeing already has a multi-year contract with Canada for the RCAF Chinooks and RCAF C-17 for support and maintainance. What's Canada going to do? Buy more expensive transports? Thirdly, Trump has told Trudeau he has to buy US or NAFTA is torn up. So Canada will have to buy the LMT F-35's.
Canada has no choice