US citizen visiting Canada - time limits

Hello,

I am a US citizen and my understanding is that I can stay in Canada for up to six months at one time on a visitors visa. Is there a maximum number of months that I can stay during the year if i was to make multiple trips. For example, if I stay for four months, leave canada, and then re-enter canada again, can i stay for another four to six months on a visitor visa (bringing the total to 8 - 10 months during the calendar year)?