Thank you for the feedback!
I could swing a charcoal Sumuelsohn suit, but I think I'd rather add it to my savings as I'm 23 and starting to build for the future.
Are the AE Park Avenues a bit too conservative for a 23 year old young man? (they are also 355$ +15% tax which seems overpriced for AE?) I believe the wedding will likely be a touch fashion forward and I am generally a very "outgoing" person in terms of my daily wear style (bright colors, slim cuts, etc).
Unfortunately in Montreal we have very limited selection in shoes/shirts etc. I would like to keep the shirt not too expensive as I will likely have to get it tailored due to my body shape (I have a 42-44 shoulder with a 33 waist). This is really on the high end of what I would like to spend http://www.harryrosen.com/eng/products/dress-shirts-ties/dress-shirts/martini_solid_dress_shirt?11210374
So a white shirt and a grey tie it is I think It should look fairly sleek. I was originally thinking green shirt (fade from light to dark) with light grey tie (bad idea looking at it now)
The AE Park Avenue is a conservative shoe and it's certainly not sleek. The problem is that black stitch cap oxfords really are the proper shoe to wear with a suit. I'd keep the shoes conservative and well shined; a slim cut suit will be sufficient for what you want. The tax is a bit more than in the U.S. but $355 is not a terrible price unless you are buying on sale or getting AE seconds.
You can get a decent dress shirt for far less than the example you cited. If you're getting it tailored anyway, even the full retail price of $88 or so for a Brooks Brothers shirt should be pretty doable. Just make sure you get a fit that looks good on you in the shoulders / chest. You can at least partly fix the rest.