Hi Mauro
Canadian canoes have a lot of advantages. Easier to get into and out of, can carry a lot more gear for camping and you can travel solo or with other people. As a kayaker myself, I think there is a learning curve involved in paddling a Canadian single-handed.
Conventional double sea kayaks are not designed to be paddled solo.
Have you considered a folding kayak?
Many skin-on-frame kayaks offer the advantages of Canadian canoes.
The market leader in such boats is Klepper. The Aerius 2 starts at about £1700. These can be paddled solo or double without much difficulty and can carry loads of gear. Also they are foldable for easy storage and transport. They are very versatile and seaworthy craft. I wouldnt care to take one on a whitewater river though.
A rival to Klepper is Pouch from the former East Germany. These have a poorer build quality to the Klepper but are still good. These are easy to get second hand from Germany. I picked one up on Ebay from Germany (try the German version of Ebay
www.ebay.de and do a search for faltboot) They go for about Euro 250. The RZ85 is the Pouch equivalent of the Aerus 2. My boat is great on the water but hard to assemble so I keep it permanently assembled.
Having said that my next boat will be a Canadian.
Paddling with children can be challenging but rewarding. They get bored and frustrated very easily so shorter trips are better. They have to be dressed for immersion in case of an accident and this makes it even more uncomfortable for them. It just takes one bad experience and they wont want to go paddling with you again!
The safety issues involved in paddling with children are enormous.
Whatever you do I hope you get some kind of boat - life is a million times better on the water.