I have not been following the writings/speeches of David Suzuki as I do not study environmental politics. However, he seems to have crossed over to my territory: xenophobia. He criticized Canadian immigration policy as "we plunder southern countries by depriving them of future leaders," which might sound somewhat reasonable (more in a second). However, he also said "Canada is full, too! Although it's the second largest country in the world, our useful area has been reduced." That second part is so chock full of stupid that it makes the rest of his statement quite tainted.
Yes, if the advanced countries of the world set up immigration policies intended to lure the best and brightest to Canada, then Canada is doing less developed countries a disservice. One can criticize immigration policies for having negative impacts on other countries. I think the issue is more complex than that, as the possibility that the best (smartest, most trained, most talented, whatever) might leave can serve as a brake on governments from pursuing bad policies. If they cannot exit, a key restraint on bad (or worse) policy policy is gone. The article that discusses this also mentions remittances--that the immigrants tend to send income back to the homeland. Indeed, remittances have become a major source of income in less developed countries. Anyhow, still, one can debate the pro's and con's of immigration policies that might entice the skilled to leave the countries that need those skills.
One cannot really debate that there is heaps of room in Canada. It is one of the most underpopulated countries on the planet: 2nd largest country with 33 million people. Even if one were to exclude from the math the various territories that are not so inhabited or inhabitable, Canada is a big country with lots of space. Sure, Toronto and Vancouver are facing significant pressures because of the flow of immigrants, but there are plenty of smaller urban areas in Canada that have room for immigrants. The country has heaps of fresh water and energy and food. The immigrants are mostly coming from places that lack fresh water and energy and food. Which is better for the global environment? Keeping people where there is scarcity? Or letting some to move to where there is abundance?
I am not an expert on the environment, but claims like what Suzuki has made suggests that he is not either. Out of space? Canada? Looks like intolerance of foreigners to me... and that would be xenophobia. Perhaps Suzuki is not a xenophobe, perhaps he just sucks at math.