I have a 46 sized u-can-do and it says the biggest 4-stroke size to be a .70. I have a XL .80 and a XL .91 4-stroke and was wondering if either of these engines will work or will they be to much for the plane? If either engine will work in your opinion which will be the best to use and what prop should I use?

check out and read the massive 28 page ucando3d .46 thread going on in the 3d section .. your question is already answered there on basically every page.

http://www.rcuniverse.com/forum/m_81..._1/key_/tm.htm