I agree with everyone else, get a 2 horse, it will do just fine.
Probably, note I said probably go as fast as with a three.
Scotty from SmallBoats.com

In case you need one, I have some of the Neptune 17lb Mighty Mites that were
returned for warranty back in 91. Excellent little motors. Not to be confused
with the "weedeater" type: Tanaka, Cruise N Carry etc. throw away motors. Also
bought all their new parts. I use one on my canoe all the time (side bracket)
I run upstream a ways from put in point and float back down. Saves having to
shuttle vehicles & I can go alone. Contact me off group if you need one. Greg
Sefton

"Mike Brannon" wrote in message news:5i8Sb.10129$tP1.5124@fed1read07...
"Walt"
Im thinking about putting a small 3.5 hp 2 stroke outboard on the square
tansom of a 16 foot long canoe.
(snip)

Once upon a time I had that exact arrangement. A 16' square sterned
homemade canoe with a old sears 3.5hp Eska pushing it along. I pulled the
thin plywood floor out and poured in two part foam to make it stay on top of
the water. Then added a sheet of new plywood so we could stand up while
inside(tricky). The boat weighed about 100 lbs I think. The motor was
around 45 lbs. I could easily car top it on my old '67 Valiant to Newport
Bay, California and back. Ugly but it worked. My brother and I would take
our fishing gear a cooler and "tuna sandwiches" out through the jetties(like
gilligan) and park off the beach for an afternoon fishing. Fully loaded it
would make around 6mph...light maybe 7 1/2.. For protected water family
picnic boat to explore a lake or calm harbor with the kids..it would be
great fun..just keep the kids sitting still, afterall it is still a canoe.
best regards, mike

You make a great point actually for the smaller engine. I heard once
that the old quote "he who hesitates is lost" was said of someone who
was going to turn a one way motor around for "reverse" having stopped
or slowed with the thrust to the side, creating a lot of leverage and
rolling the boat. Sounded good to get it going over. I might want to
have the smaller engine anyway in case the throttle gets away with you
in a unforseen situation like bottom contact or a slip.
Scotty

About the rolling effect ... I had a mere 32 lb thrust on my canoe and tried
it ... it would have rolled for sure. And the thing about a paddling canoe
.... it is designed to track straight which is what it does so the tendency
is to oversteer in an attempt to get it to turn ... and all that happens is
.... nothing ... until you hit the 90 degree point and then there is a real
danger of rolling it. With the electric, I'd just lock it and steer by
leaning or using the paddle. I went with the regular kevlar canoe ... was
mainly into paddling smaller waterways but the motor was great to have for
cruising or getting back home.

"Backyard Renegade" wrote in message
om...
"Mike Brannon" wrote in message
news:5i8Sb.10129$tP1.5124@fed1read07...
"Walt"
Im thinking about putting a small 3.5 hp 2 stroke outboard on the
square
tansom of a 16 foot long canoe.
(snip)

Once upon a time I had that exact arrangement. A 16' square sterned
homemade canoe with a old sears 3.5hp Eska pushing it along. I pulled
the
thin plywood floor out and poured in two part foam to make it stay on
top of
the water. Then added a sheet of new plywood so we could stand up while
inside(tricky). The boat weighed about 100 lbs I think. The motor was
around 45 lbs. I could easily car top it on my old '67 Valiant to
Newport
Bay, California and back. Ugly but it worked. My brother and I would
take
our fishing gear a cooler and "tuna sandwiches" out through the
jetties(like
gilligan) and park off the beach for an afternoon fishing. Fully loaded
it
would make around 6mph...light maybe 7 1/2.. For protected water family
picnic boat to explore a lake or calm harbor with the kids..it would be
great fun..just keep the kids sitting still, afterall it is still a
canoe.
best regards, mike

You make a great point actually for the smaller engine. I heard once
that the old quote "he who hesitates is lost" was said of someone who
was going to turn a one way motor around for "reverse" having stopped
or slowed with the thrust to the side, creating a lot of leverage and
rolling the boat. Sounded good to get it going over. I might want to
have the smaller engine anyway in case the throttle gets away with you
in a unforseen situation like bottom contact or a slip.
Scotty