It depends on the tour.
If I fly in to a warm-weather location, touring in January and February is great. That time of year isn't so good in places like northern Saskatchewan where it will be cold and snowy or the Pacific Northwest where it will be cool and rainy.
On Vancouver Island, any time from early spring to late fall is great. Inland, the middle of April to the beginning of October is good. In the Arctic, July is phenomenal, if for no other reason than to experience the midnight sun.