Being a seasonal resident, see
http://www.cbsa-asfc.gc.ca/publications/pub/bsf5082-eng.html#s3 with your own home or a 36 month lease only gives you the right to import furnishings one time without paying duty or tax. It does not actually give you the right to live in Canada.
As a US citizen, you may stay in Canada for up to 6 months a year unless immigration decides otherwise. That is, immigration can at any time decide that your intentions are not to stay in Canada temporarily, that you are a risk to overstay or planning to work illegally and then can decide not to let you in.
To live in Canada permanently, you need PR. If you were to decide that you want to live in Canada for up to 6 months a year as a visitor and cross the border every day, you should apply for a Nexus card because it makes your border crossing a bit easier.