Mapsource from garmin doessn't give topo maps because;
topo maps have to have been created by a source such as the DNR who do the surface research which would very unlikley be inclued in Mapsource.
What you are looking for in a GPS, is one that reads the 3 formats of Co-ordinates used to find location by satelite.
I'll give you an example of a GPS that does this and its the Garmin Nuvi. You can be in the middle of a lake have your Nuvi on and want to mark that spot as a good fishing location. You can hit save and go back the next day and find the exact GPS co-ordinate locations and fish the same spot. This is something commercial fisherman have been doing for years, if i'm not mistaken Lowance came out with the original technology after Pres. Reagan released the private use of the satellites put in space after the Star wars Program. GPS itself can't give you topo readings of a lake. Use a depth finder on you boat, co-ordinate and mark the depth yourself to create a map for yourself. No DNR is going to take the time to mark an ever changing surface for your use.
SO; use a depth finder for bottom topo and a Nuvi (I mention this model because I know it does co-ordinates) to mark the spot. You need to do a paper makeup of the location you just charted then go back in a month and see how much it has changed to see how futile it would be to try to make a map for your convenience. Sign up to this link to learn from the best about GPS use; Layin' down tracks - ADVrider
PS, that GPS, Cadillac put in their car to pimp the item off as a great idea to get your old lady to have you spend way more than you make for nothing is not what you're looking for (it'll more than likely lead her and the kids down some street they shouldn't be on in reality).
Great GPS technology is a tool to be used with other tools that take work to get results. Gettin your kid to soccer isn't one of them that rate high on the charts :-)