Truces are an excellent form of strategy, being able to negotiate with other people is what separates playing against people and playing against machines. People who don't like truces are probably people who have no diplomatic skills.
The main thing to watch out for I would say is being absolutely clear of what your proposing, for instance with a truce give parameters, either set an amount of turns it will last stating the round it ends on or make it continuous with one turn to break for example.
In your case a simple "i'm not interested in canada and will withdraw my troops next turn" will do, it doesn't require an answer that way and blue can do as he pleases. This offer isnt a truce however so there is every chance your just feeding blue a bigger army that will come after you.
Don't take it badly if an offer is refused, if somebody breaks an agreement don't bother getting into a verbal rally just state in the chat your truce has been broken and make use of the feedback system to discredit the dishonesty