You are making a common misunderstanding, namely that you can decide if your daughter is a dual citizen or not. That is not the case.
Assuming that you (as the Canadian parent) were yourself born in Canada or received Canadian Citizenship by applying for it and you were a Canadian citizen the day your daughter was born, your daughter is automatically a Canadian Citizen. You can't choose if she is or not. Similarly, since her dad is US-American she will also have US citizenship. Again, this is not a choice to make, the moment your daughter was born, she was a Canadian and a US citizen.
You can decide if you want to apply for her US and/or Canadian passport. Note that if she has US citizenship (which she does), she MUST use her American passport to enter the US. She can't enter the US as a Canadian. Again, this is not a choice to make, she is a US citizen, so this is how it needs to be done.
Note: There might be some very specific circumstances due to which she did not get US or Canadian Citizenship at birth (for example, in case one of the parents works for the diplomatic service), but those are very special cases that don't apply to most people.