Canada accounts for only 1.6% of the world's total GHG emissions. Of that 1.6%, the oil sands make up 10% of Canada's total, meaning the oil sands make up only 0.16% of total global GHG emissions.
https://www.nrcan.gc.ca/energy/publications/18731Let's say by miracle Trudeau somehow soon cut oil sands production by a third, that would reduce global GHG emissions by only about 0.05%
Cancelling the pipelines won't have much effect on reducing GHG emissions since the AB oil will still get where it needs to go by truck or rail, it will just be less efficient & more costly and probably produce more CO2.
People overestimate how much effect Canada, a country of 36 million out of 7.5 billion, can have on reducing global GHG/AGW. It's not nothing, but it's not a lot either. Doesn't mean we should do nothing, it means it makes little sense if we strangle our economy to take bold action while the US and China doesn't follow suit.