People are assuming that the Europeans (and particularly the British) will want the canal that bad - IOTL, the British only got a fetish for holding the canal after they were forced into Egypt by their first, second and third preferences for resolving the crisis falling through. (At the time, the British wanted the Ottomans to intervene, the French to intervene, or to arrange some sort of multinational intervention including at least France - the UK intervening alone was seen as expensive and burdensome and given how the UK already had everything she desired in Egypt through indirect economic imperialism, the government of the time had a point.)
For Venice, Egypt was already a key trade route for spices from the Indian Ocean making it into the Med - they'd tried several times to gain control over that route, both by attempting conquest (unsuccessfully) and by signing favorable trade deals with the Ottomans (very successfully). Genoa likewise was trying to do the same things (less successfully than the Venetians). I don't see how the existence of an Ottoman canal would give either city state more impetus (or more resources) to conquer Egypt. Nor do I see any reason why a canal would encourage the two city states to work together more than they did.
Further, I don't think people are appreciating just how powerful the Ottomans were compared to Europe before the reverses of the late 18th through the 19th Century. They certainly weren't invincible, but they did have a large population, a relatively tolerant and innovative society, an advantage in accessing strategic resources (the forests of the Balkans allowed the Ottomans to build ships and indeed whole fleets with a scale and endurance that Europeans powers around the Mediterranean could not match) and a large and fairly difficult to invade territory. So while it is quite possible for the Ottomans to lose any canal they might build in Egypt, I think it is highly unlikely for any likely coalition of European states to hold the canal for more than a generation or so. At least before 1800.
Also, any canal that is built will be dependent on the Nile river for its water supply (even the modern Suez canal needs water from the Nile to function). That means holding the canal and keeping it functional requires holding at least a portion of the Nile delta.
I suspect that the main impacts of the canal if it were built would be to strengthen Ottoman naval power - with a canal they can move fleets from the Indian Ocean to the Med/Black Sea. Given the distances involved, I don't think that in itself will be huge. The bigger impact will be that with a canal, the Ottomans can build ships in the Balkans or Anatolia and sail them to the Indian Ocean, making it far cheaper to build fleets in the area (OTL, they transported the naval supplies over land and built the ships on the Persian Gulf or the Red Sea).
As people have already pointed out, a big part of OTL's Suez canal's utility depends on ships having steam or diesel power. Without those, naval travel in the Red Sea depended on oars, which required a large amount of skilled labour.
I'm not sure if the canal would, in the end, have repaid its investment to the Ottomans. Certainly if it did prove worthwhile, it would be very marginal.
More interesting would be a Suez canal built in the 1800s, 1820s or 1840s. For example, with the earlier dates, we might see the canal built, fail financially then be left to decay. Would someone try to build the canal again if there had been a failed canal only a generation or two before? Or what about a canal that is built just as the very earliest naval steam engines are coming on line? Might steam tugs be designed to work in the canal and the Red Sea and thus lead to an acceleration of marine steam technology?
With regards to colonialism, I'm not sure there would be much difference from Suez itself. The big thing that drove colonialism in Africa was the British intervention in Egypt - that depends not so much on Suez as how the government of Egypt manages its debts.
fasquardon