Is it safe? There are hippo everywhere else in Africa.
That is exactly why this is one of the very few places you are permitted to do it. The Momella lakes have no hippo and no crocodile because the water is alkaline, and Arusha National Park has no lion. It is the safest water activity in northern Tanzania, which is why it is the only one.
How fit do I need to be?
Not very. Two hours of gentle paddling on flat water, and you can stop whenever you like. Shoulders that object to repetitive movement are the only thing worth mentioning in advance.
Can we do this and a game drive on the same day?
Yes, and it is the best way to use it. A morning canoe and an afternoon walk in Arusha National Park makes a genuinely good day, and you are back in Arusha for dinner.
Which is better, Momella or Duluti?
Momella, if you have the time and are happy to pay park entry. Duluti, if you have arrived that morning, are tired, and want something beautiful and undemanding half an hour from your hotel.
When is the best time of year?
It runs all year. Mornings are calmer and clearer, wind gets up later in the day, and the clouds usually take Kilimanjaro by mid-morning. Go early.
Is there anything like this in the Serengeti or the Crater?
No. There is no canoeing in the Serengeti, Ngorongoro, Tarangire or Manyara, and there will not be — it is a combination of hippo, crocodile, lion and park regulation. Arusha National Park is genuinely the exception on the northern circuit.