Boeing looks at it this way. They drop the trade case, the Canucks buy 18 F-18's and they potentially lose hundreds of 737 sales. 

An F18 Super Hornet cost around $55M X 18 plus spares etc - $1.5B
The 737 Max starts at $90M and goes to $110M - so average it at $100M. If Boeing lose 100 sales to Bombardier that's $10B. Add in spares and it's around and it's $12B - $13B. And what happens if the number of lost sales is really 200 - 300?

Pretty easy to see that Boeing aren't going to drop the trade case.