Just a personal opinion, your are saying that both of you will be american citizens; my advice for you is to stay in the USA and that is enough.
I am wondering why people who have a citizenship from countries such as; UK, USA, Australia, want to get another citizenship !!
Note: I am speaking for myself.What you think is not true. It is not the citizenship that pull's us. There are various other factors e.g Family togetherness, affordability (Bigger Houses), better and secured environment, future of our kids etc. to mention just a few. I could go on and on.
Canada is not a cheap country, it is more expensive than you think, so bigger houses......etc is not that easy. (i have been living in canada for more than one year)
In general, all of the developed countries almost have the same level of security, income.....etc otherwise, they wouldn't be a developed countries. so the future for you, your kids and family will be the same in any one of those countries.
Is that a kind of habit to collect as much citizenships as possible ?
No, but why not? If you contribute to various aspects of a country you have lawfully lived in as a good citizen, then, Why not, if you qualify? Secondly, when you live in a country for quiet sometime, you kind of invest a lot of things into that country and then you want to be recognized for that and of course don't want to loose it.
That is great, you said, when you live in a country and contribute in their economy (or if you are ready to relocate to their country and live there as a bonafide citizen), absolutely you should be more than welcomed to get their citizenship and achieve their social benifits, but if your intention is to get another citizenship, so you will not be able to be a real citizen who is eligible for all of the available benifits because you will leave that country to another country to get their citizenship..... and so on.
Therefore, you will be a citizen of each of those countries only by name but not eligible for every benifit in the country, and not even familiar with the country since you hav not lived there for enough time because you are trying to comply with another country requirments regarding the residence, eligibility.....etc to get their citizenship.
When you concentrate all of your efforts in one country(the country that you really selected to live in, you will pay all of your efforts and do your best to serve that country, and they will give you the maximum level of protection, social benifits, and sometimes if you are interested a very important positions in the government at that country might be available for you.
For me i selected canada as a choice just because it is the easiest one of them for me to immigrate.
Fine, everyone's situation is different. Believe me, If the CIC says to me that we have only one Visa left and there are 2 of you who qualify for it. You qualify more because you applied just a day before the other applicant who is but from e.g a war stricken zone or country and I had the option of choosing ( i.e if I knew) who to give it to, I will tell them to give it to the other person. I hope you get my point. Unfortunately this is not the reality. There are enough visa's and such a situation will never arise.
At the end, that was my personal opinion so please do not feel bad toward my words.
Hope the best of luck for all of you.