Trouble is, if Ford says no to that trade off, what can the workers do?  They can strike when the time comes, but that’s a gamble, given that Ford is already saying that the Canadian operations are too costly.  Ford could feasibly respond to a strike by moving the work elsewhere.  But should the workers just keep giving up their wages and benefits in the hope that Ford will stick around in the long run?
What would you do if you were a Ford worker?  Agree to a large cut in your pay and benefits in the hope that you still have a job a few years from now, or refuse concessions, keep your pay and benefits for as a long as you can, and hope that Ford doesn’t lay you off?