If you need good IQ, you cannot beat D800. But for that, you have to get Nikon, as Canon is stuck with its 10 year old sensor tech. Since Canon sales are good, they have no incentive to use better sensors. Unless you are stuck to Canon due to financial/equipment commitments, Nikon is the better bet at this time.
Troll. Do you really feel like 36MP is necessary? Unless your're printing in feet instead of inches, it is completely unnecessary. Also, if you're referring to Nikon's perceived high ISO image quality it is a moot point to an architecture photographer who shoots at native ISO (100) about 95% of the time.
How about Nikon's mediocre (compared to Canon) and outdated PC-E lenses? What? Nikon doesn't even manufacture a 17mm lens with shift? That's a shame.
I'm not tryin to be a fanboy, but Canon is clearly the better choice for architectural purposes.
Canon's latest sensors are simply outdated in terms of detail resolution. You cannot bring superior images out of mushy low ISO capabilities. And 36mp for landscape/architecture is NOT overkill. LF, which is the ultimate choice of pro landscape/architecture photogs, goes to hundreds of equivalent MPx. And MF backs can yield 60+ MPx.
Basically, 36mpx is not enough when detail is needed. Canon is simply either incapable of bringing something to the market at competitive pricepoints, or they are milking their fanboys for their worth. Either way, it does not look good to impartial customers.