I find it easy, others find it difficult. Some actors hire vocal coaches. I think that since I am musically inclined and have a good ear that it helps with accents. If you look at some actors, such as Hugh Lawrie (spelling?) and Nicole Kidman, they seem to be able to speak with an "American" accent for a role, yet have their native accent when in normal conversation. I guess it's just something that takes practice to perfect.
Since I just got permission to work in Canada I am going to apply for a permit and then submit new head shots to some casting agents in hopes of finding an agent up here. I guess then I'll find out if it is hard to work in a non-native tongue or if I will just have to accept roles that are only English speaking. Either way, I'm looking forward to it.