ok i do quite a bit of this sneak up stuff.
1. I am not sure about sneakin up on them on the water with a canoe will work. it might be too slow and too obvious. when you start down the river at them the birds will see you comin streight at them.
2. Heres what i would do. i would just slowly walk up to the river util i get about 200 or so yrds away. make sure that you dont get too close to spook the ducks and stay out of there sight. then crawl on your belly until you get the last part of grass or shore line and ducks are prty close. some times i just lay still and the ducks start to swim up to the bank and then shoot or slowly crawl alittle more then get up and shoot.
3.this hunt will work alot better with 3 or 4 people at least 2 people should sneak up on the ducks and what ever way you sneak up on them the ducks should fly the exact opposit so take one other guy down the river aways and put him there and if you got 4 take the other guy to a different spot so if you get a duck and the other ones get away they will fly right at them. we use this technique often also and have good luck using it. this is how i would do it but i am not sure what the terrain looks like so i cant say that this will work. you will have to find out how you want it by lookin at the land. hope you get some ducks