It's true that there is an insufficient supply of technology talent in Canada, but that is also true in the US. Anywhere they go is going to have this problem.

In northern California, the vast majority of tech workers are from other states or other countries. It's going to be a given that a big company looking to build a new campus anywhere will be expecting to import a lot of people to fill the jobs they are creating.

In fact, if I may join in the speculation for a moment, I feel like the only reason Amazon would seriously consider Canada as a candidate for HQ2 would be immigration policy. The US caps the number of H-1B visas it issues each year, and there is a threat that the current government might make it even harder to get them. In Canada it is easier to bring someone in as a TFW, and the government has lately been making it more appealing by removing time restrictions on the visas.