For suits and shirts, Moores is a solid choice.
For shirts, you can also try the 8th floor of the Bay store downtown.
For shoes, there are plenty of choices.
You can try:
. Global, which is in the basement of Place Montreal Trust,
. Payless chain stores, which are located in Eaton center metro level, Alexis Nihon Plaza metro level in Atwater area, Place Cathethral, etc.)
I am currently working in a computer consultant company, which is located in downtown. I may pass you some tips. If you don't have to work on-site (client side), one suit should be good enough, in case of business trip or company events. Monday to Thirsday, dress pant or casual pant and dress shirts, Friday you can wear jeans. It is not mandatory, just FIY. One of my teamate always wears jean. I only one time saw him put on shirt because the project manager came to visit us. Enjoy your shopping!