Having worked in Canada on the TFW programme and now a Canadian P.R. with a T.C. ATPL I can see both sides of the argument. Having said that, I think the domestic Canadian pilots are right. Canadian carriers should employ and train up their own pilots.
The seasonal flow of pilots to/fro Europe may help the balance sheet for the TUI group but it's not fair. In Summer Canadian pilots are "taking jobs" from UK & EU pilots during their company exchanges. Incidentally, some Canadian pilots have also had too much single malt in the UK as well.
May I propose a compromise that the Commonwealth Freedom of Movement Org. (cfmo.org) is suggesting:
As the name suggests, a core Commonwealth countries open market for law abiding people. Similar laws, cultures, ancestry, history, values, religion and outlook on life.
A member of the Canadian cabinet told the BBC last Summer; "we're family" as the Brexit woes were being discussed. I think this idea is slowly gaining traction.