Book the Fairmount Royal York hotel, and ask for the Luxury Executive Suite or even the regular One Bedroom Suite.
Its about 1200-1300 square feet, includes a living room and a separate dining area and a bedroom that is really about 2 or 3 times the size of regular downtown Toronto 4 star hotel rooms. Those suites come with two bathrooms.
It would easily fit 20-25 people comfortably and it's not overly expensive.
Or go big and hit up the Ritz or Trump.
Their corner executive suites have unbelievable space, just make sure you speak to them about room specifics, some of their suites are designed kind of awkwardly, space-wise. Not all are geared for larger parties.
Or the Intercontinental by Simcoe & Front, ask for the Bi-level executive suite. Two floors, a staircase that wraps around with enough nooks and crannies to get creative.