If you purchased a Cond and did not know that the building was 90 % owners who rented their units out and you were not informed of this, is it legal?

I don't suspect it's illegal. When a new condo sells their units they don't have to ask whether the buyers will live in the unit or rent it out. So the builder will not have that data. Having said that, a local realtor may know if most units will be owner occupied.

If you are talking about a resale, this information can be found on the status certificate prepared by the management company on behalf of the condo corporation.

In BC, part of the due diligience would be examining the Form B Certificate, which is a document filled out by the property manager. One of the required fields indicates approximately how many units are currently rented out.

Your Local Realtor and Status Certificate can find out the ownership.I think it is not illegal to have more renter than owner.

The owner to renter info is found on a status certificate.

When people purchase to invest... often units are rented out. Some builders do ask if you will be renting or purchasing to own, or flipping. However that doesn't mean you have to do any of those... and at closing you can change your mind. It helps the builder determine some GST / HST credits if you are going to flip that you aren't eligible for. But if you are buying resale... the status certificate does tell you what percentage is rent or not.

Did you read the status certificate or your lawyer did? If he did then go after him.

Status certificate has the information you are looking for. You may choose to talk to your lawyer and review the information.
Some condominiums have different set of regulations in place regarding Rentals,Pets,...Etc.
Consider all Condo rules before buying.

If the unit holders abide by the condo rules what is the difference between a family that owns and a family that rents?