Tbere's little evidence to support that. Surveys have been done to determine the number of vacant homes in several markets and it always turns out to be a pretty low number. And that includes reasons other than investment groups choosing to do so.Actually the third reason matters most. Globally, investment groups are holding onto trillions of dollars worth of housing with some of it being left intentionally empty. They own so much residential property that it's worth more than the US GDP in a good year. The fact is that housing costs have skyrocketed by design and govts are complicit in it. The IGs buy up homes and then rent them out for rather more than what the mortgage payment would be if an individual had been allowed to buy it.
The govt announcing that it will build thousands of new homes is pointless unless they change the fucking laws to prevent IGs from buying them up.
I say it's by design for good reason. For the middle class home ownership was a way to build equity and wealth. For many it's the only way. But your govt doesn't want that as evidenced by their reticence to do anything about the problem. Did I say reticence? I meant payola. Trudeau bloviating that "housing is a right" is just more of his blowhard bullshit that he doesn't actually mean. It's just sweeet talk for the proles to get their votes.
These IGs have also been instrumental in the removal of rent controls. Nor do they want anyone (but themselves) owning their own homes. You and I and anyone else in the "working class" owning their own homes are in the way of their ability to make even more astronomical profits and they're not going to stand for it.
Building a bunch of housing without changing anything in the laws will simply result in investment groups ultimately getting their hands on it.
Consider vancouver, one of the most expensive areas in the country. As you can see, vacant homes are a pretty small hunk of the supply:

Empty Homes Tax reduced Vancouver's number of vacant homes by 36% | Urbanized
Five years after the City of Vancouver rolled out the Empty Homes Tax, the number of vacant homes has fallen by 36%.

Further, if we built enough houses they can leave ones empty if they like and it really won't matter. Jack up the taxes on empty homes like bc did and voila - they're helping fund the provincial services while losing money on a slowly appreciating asset. If there are enough homes then there is little incentive for investment groups to buy them up because they won't appreciate in value fast enough to make it worthwhile.
In the end it all comes down to having enough homes. And we don't.