I understand your concerns with the auto industry as it's the largest export sector for Ontario. It's not an ideal situation to be in but Canada is forced to respond in kind to actions by the US.
If your point is for Canada to just accept annexation, then sorry to say but it's not something many Canadians are going to do willingly. Maybe this is a point of difference between some recent immigrants and old stock Canadians. Recent immigrants often come to Canada for better economic conditions. For many old stock Canadians there's alot of pride for the country not being part of the US. It maybe considered stupidity to resist but really depends on the lens you see this through.
It's true that Canadian market is not very unified due to the protectionism between provinces. There's tariffs between provices and barriers to building pipelines connecting the nation but due to the current trade war with the US, reforms are likely to come. There's alot more political will for change right now, even against entrenched interests.
Expect times to get tougher and Canada to explore other economic partners. It's likely that Canada will resist annexation and continue grassroots boycott of US products that have a viable alternative.
To me, the annexation talk is just a red herring.
Get people to talk about that, then do the dirty work, when everyone's attention is focused on something else.
This squabble, between Trump and all of Canada, reminds me of what Kissinger said about the Chinese.
I believe Kissinger was an historian. Maybe he was a political scientist, but he knew history. He probably studied Chinese history in depth, on his own.
What he said once, was the Chinese politics, they find a way to survive, because they were in all sorts of situations, whether strong or weak, and they had plans that eventually found a way to keep the country intact and sustained. In other words, the Chinese political establishment, in few thousand years, been in every possible political predicament we can think of.
That is the very problem with Canada today, right now.
There is no experience when bullied like this, and Canadian politician is basically doing nothing to protect ourselves.
They are just totally lost.