One of my favorite workouts is a long rollerski on the way to work. The newly paved path along the Rockcliffe parkway allows me to go almost all the from my house in the east end to Carleton University without leaving the paths. I take that path along the parkway until I get to the Rideau River which I follow all the way to Hog's Back then loop back along the canal where I end up right across the street from the building where I am working. I usually takes me just under 2 hours.
I do this workout on classic rollerskis, and as the route is mostly flat, this means it is almost entirely double poling. There are two main advantages I find to doing classic rollerskiing. First, double poling happens to be my weakest technique, and as long as you have good sharp pole tips, rollerski double poling translates pretty well to double poling on snow. Second, you take up less room doing classic than you do skating, and that makes everyone else on the path happy.
The system of paved paths in Ottawa-Gatineau seems to always be expanding and becoming increasingly well connected, so there are a lot of options for places to rollerski. The paths on the Ottawa side and along the river on the Gatineau side are mostly flat, but there are some good hills as you get up into the park.
The only drawback of rollerskiing on the bike paths is that you have to be more careful than on the wide open parkways. First, you need to watch out for other people on the paths, and make sure you stay close to the right edge of the path and give lots of room when ever you are passing anyone. Just remember that flailing ski poles are pretty scary things. As well, you have to watch out for obtacles in the path. There are the curbs if the path crosses a street or the entance to a parking lot, there are sections with bumps or holes that could catch to bottom of most rollerskis, and of course the occasional fallen tree. Finally, you need to watch out for the downhills. There are many steep, winding downhills, especially in Gatineau in the south end of the Park, where it is almost impossible to have enough control to make the turns if you are going full speed. So basically, it is best to just walk at least the top of any hills you are not sure about.
As long as you are careful, the bike paths are an ideal place to get in a ski specific workout when the parkways are not closed to cars. So get out there are enjoy the beautiful paths that this city has to offer!
Here are some web resources on the Ottawa area bike paths..