Good cupcakes or birthday cake downtown
I need to get either cupcakes or birthday cake at the last minute (tomorrow) and I need the location to be downtown (Yonge and Dundas/ Yonge and Queen/Yonge and King area).
It's not DT, but at Yonge and Eg there's the Cupcake Shoppe which I think makes the best cupcakes in town - I did a cupcake tower for my wedding and they weren't expensive. But since you're in a bind and might not make it to Y/E - then at Yonge and Queen is Senses, not sure if they have cupcakes or the amount you're looking for but they always have an abundance of fresh cakes... call and reserve one:
I was going to suggest Sen5es as well, since it's in the neighbourhood you requested, but to be honest, I find their cakes lackluster and very overpriced. You would end up spending a fortune (especially if you're going to need a large cake) on a so-so cake, but it will be pretty.
Commercial options such as Dufflets and La Rocca can be found at Decadent Desserts in The Path near Union Station and Yonge/King area. About $30 for a large cake for about 10-15 ppl.