The post by
@Natan covers it and I fully agree except the part about risking the U.S. Department of State treating use of a foreign travel document as relinquishing U.S. citizenship (at least not for the vast, vast majority of dual citizens, and particularly those who have U.S. and Canadian and no other citizenship).
My post was a response to the erroneous post that Canadians would be denied entry into Canada unless they present a Canadian travel document (Canadian passport for Canadian citizens; PR card for Canadians with PR status), not about U.S./Canadian dual citizens. Note, for example, that U.S. citizens (including dual U.S./Canadian citizens) are NOT subject to eTA requirements and can board flights to Canada by presenting their U.S. passport.
While I agree with
@Natan that when entering Canada, Canadian citizens SHOULD present their Canadian passport (noting that many or most countries generally require its nationals to present that country's passport rather than TDs from another country), in my experience and as I have seen reported by many others (including reports from people I know personally, no connection to forum discussions), Canadian border officers are usually far less picky, that is much more tolerant, about this than their American counterparts. I've known individuals, dual U.S./Canadian citizens, whose border crossing into the U.S. was delayed, and unreasonably confrontational, because they were not carrying an American passport. They were eventually allowed to enter the U.S., after being given a rather severe (and largely unenforceable) admonition. In contrast, I have forgotten my Canadian passport on occasion and have had no problem at the Canadian border presenting my U.S. passport.
(Well, actually, my wife and I previously had a bad habit of mixing our Canadian passports up, so when I have traveled to the U.S. alone, it turned out I had her Canadian passport not mine . . . until the time I did not check my passport before handing it to the Canadian border officer, and thus handed him my wife's passport as if it was mine, and was quite pleasantly surprised at how well that went . . . particularly since we do not share any part of the other's name. What I did could be considered a fairly serious violation of law (if done with intent, which it was not) and technically CBSA may have had an obligation to seize the passport. Instead, it was almost a humorous exchange, the PIL (booth) officer asking me "who is X Z?" and me answering, in a somewhat perplexed tone, "she is my wife." I am well enough aware of how serious it can be to present a passport not one's own, or for that matter to even possess it without adequate explanation, I greatly appreciated the officer's smile and friendly acceptance of my explanation, without a referral to Secondary even, but have since been a lot more diligent about keeping our respective documents separate.)
In contrast, on one occasion after handing the PIL officer my U.S. passport upon arrival at a PoE into the U.S., the officer asked me my citizenship and he got very cranky when I answered "I am both a U.S. and Canadian citizen." He asked me what my citizenship was again, and I answered "U.S." and while his tone remained cross, he only asked the usual perfunctory questions and did not refer me to Secondary (over the years, despite being a U.S. citizen presenting my U.S. passport, I have spent more than an occasional amount of time in U.S. Secondary, including some rather intense, confrontational, even hostile experiences, despite my best efforts to be polite and cooperative).
It warrants acknowledging that how the border crossing transaction goes can vary greatly depending on many individual factors, some of them rooted in discriminatory biases (which is contrary to the law both sides of the border, but recognizing that much of this is not enforceable unless it crosses a significantly egregious line and too often not even then).
It also warrants recognizing that actually the U.S. and Canada share a great deal of information about travelers, who are FNs or PRs, crossing the border going both directions. And legislation is pending which will further extend this to include information sharing about Canadian citizens as well as FNs and PRs. Note, for example (and this has long been the case regardless of citizenship), that Canadian border officials can readily access a traveler's U.S. criminal record history.