Doing this contradicts the definition and intention of "temporary visit", and it's not okay to cross back into the States and turn around and re-enter Canada by lying to an Immigration Officer about your intentions, just so that you can indefinitely extend your "temporary" status. The "understanding" would be that a genuine temporary visitor would probably need to be outside Canada for at least as long as they stayed in Canada in order to maintain a job/residence in the States. If you want to stay in Canada beyond the six months stay limit, you should file an application to extend the conditions of your stay from within Canada and pay the associated fee. Filing an application to extend the conditions of your stay gives you "implied" extended status in Canada, allowing you to remain in Canada, until a decision is made on the extension application. If it is denied, you must leave Canada immediately, but if it is approved it will clearly define the terms of your additional stay.
There is a second option to extending your temporary status in Canada that involves filing the same "Application to Extend the Conditions of Your Stay" in conjunction with an inland Permanent Resident application. If you elect to use this method, you need to file your inland PR application BEFORE your original authorized temporary status expires - and include the extension application and the accompanying fees in the same envelope with the PR application. This gives an inland applicant valid temporary status until First Stage Approval or Approval in Principle (AIP) is reached during PR processing. Many applicants using this method choose the "Open Work Permit" option on the extension application, which results in Vegreville issuing an OWP once Approval in Principle is achieved. More information on this process is included in the Inland Applicant's Guide, Part II, Your Status in Canada.
There is a second option to extending your temporary status in Canada that involves filing the same "Application to Extend the Conditions of Your Stay" in conjunction with an inland Permanent Resident application. If you elect to use this method, you need to file your inland PR application BEFORE your original authorized temporary status expires - and include the extension application and the accompanying fees in the same envelope with the PR application. This gives an inland applicant valid temporary status until First Stage Approval or Approval in Principle (AIP) is reached during PR processing. Many applicants using this method choose the "Open Work Permit" option on the extension application, which results in Vegreville issuing an OWP once Approval in Principle is achieved. More information on this process is included in the Inland Applicant's Guide, Part II, Your Status in Canada.
As mentioned earlier, it's understood that the maximum time a temporary resident from a visa-exempt country is allowed to remain in Canada is six months, so if you want to stay longer you're required to apply to extend your stay. Unfortunately, many US citizens in a relationship with a Canadian citizen, don't honour the "six months stay" limits and believe they can simply leave Canada and then turn around and re-enter immediately to "start the clock" again.