The train is quick and easy. It has a stop at Dorval, near the airport, and arrives close to downtown Ottawa. The airport is a lot farther and the cab fare is substantial. There is a transit bus that's actually faster than the cab in Ottawa. The thing to consider is that the train is not affected by weather in Montreal or from wherever you flight is coming from. Scenery from trains is what you think it is - the countryside has terrain that is not the same as other places - if that is interesting.