In all honesty, a significant portion of immigrants from outside the EU are Indian (9% by birth). Super educated, very intelligent and will work for a pittance compared with locals. All part of a trade deal and what both sides want. Can't see us buying wheat from India though. Can you?
Even with WTO tariffs (as they would be when go, but Canada can choose to not enforce them), I believe it's still cheaper than what we get from Spain in part because of the limited capacity with the EU markets pushing prices up while punishing those who want to go outside.
Obviously, there are standards to be met, but it's up to the UK to legislate and identify what appropriate standards we are to keep. Take a look at how chickens and pigs have been kept in Holland compared to the UK. The conditions are not so good, so be careful to check where your meat comes from if you care about animal welfare!