That is a fairly naive stance. Of course no Canadian official is going to call his Malaysian counterpart to tell on someone (though it could happen). Think a bit more laterally; when you renew your Malaysian passport you will have to answer the question of whether you have acquired another citizenship, or whether you are a citizen of another country. Sure, you could lie, but that has consequences. What if you get stopped at Malaysian immigration next time you enter the country and are asked, or indeed searched? There are many permutations of these scenarios.

I have not read the Malaysian immigration act, but I'll bet that the act of acquiring Canadian citizenship automatically revokes Malaysian citizenship. That the person still holds a passport (which, by definition, is at that point invalid), is an anecdote.