"I'm here for business" is pretty vague. Maybe it works. But if pushed, "I'm here for meetings" is very different than "I'm here to train my team" or "I'm here to complete a project.". The second and third statement could imply that you or your company have elected to 'take' (true or not) work away from the local workforce. That may cast you in a bad light.
Not to belabour the point, but a Canadian entering Canada doesn't need to play this game. The CBSA does not have the authority to stop him coming into Canada. All he needs to say is "I'm here!" (I'm leaving aside customs issues and instances where the person has a long list of outstanding arrest warrants, though even in those cases the Canadian must be admitted into Canada.)