If you ask people to vote on mass immigration (not immigration that benefits the nation, mass immigration that benefits the corporations), the vast majority will be against it (brexit was ultimately about immigration for example) because it takes jobs, pushes down wages heavily, pushes up prices of and lowers availability of houses and rental property, causes issues for health care and destroys social cohesion.
This is viewing Canadian culture from UK pov imo.
Back in 90s to early 2000 Canadian housing prices weren't nearly as high. And healthcare system issues only start showing in past 5-6 years or so. (It was always very inefficient back then, but not 27 weeks wait time level of inefficient). So the negative aspect of mass immigration wasn't showing. People had way less reasons to be against immigrants 10-20 years ago.
There are no such thing as "destroys social cohesion" because multiculturalism(or people call it cultural mosaic) has been THE core Canadian value since 1971, when PM announced that it is the official government policy. You can't destroy social cohesion if the core values of a country is multiculturalism(in other words, social cohesion is weak to begin with, nothing to destroy). Ever since then the entire education system teaches people to accept immigrants and embrace multiculturalism. This shapes many people's pov on immigrants in Canada.
So there is very solid historical factors affecting people's opinion on mass immigration in Canada. It is not some random research facility making things up. This is also likely a different scenario from the UK since UK doesn't have the same history nor policy. Hence different pov on the whole matter.