Windrush has nailed it. Don't forget to stop at farmers markets and buy fruit. Do not try to take that fruit back to the U.S. with you, they don't like it.

There is also the full (100 mile/160km) circle ride where you don't take the dinky little ferry but ride all the way up to Fort Erie and then down to Niagara Falls. It's paved trails all the way, and (with the exception of (parts of) the bit between Niagara Falls and Niagara on the Lake, it's surprisingly empty. Pick up a bike map at a bike store or at a tourist office. It shows all the trails and the quiet roads, and it even shows the hills. There are not very many hills, but getting up the escarpment is always something of a challenge.

I wouldn't bother switching the computer. Just add 50 percent to the number of miles, and you will be pretty close to the number of kilometers. So 10 miles would convert to 15km. (It's actually 16km, but it's harder to multiply by 1.6 than to multiply by 1.5, and who really cares about the difference)