Easyfill will do the job just feather it out about 300mm. If you are not particularly skilled it is one of the easiest to sand down afterwards. The only problem you may have and this will apply whichever solution is used is if the join does not have reinforcing tape or scrim then cracks may keep coming back. Try to tape the join if you are not sure the self adhesive type is probably the easiest to work with.

Richard