If you intend to still work in the States while your application processes, I'd honestly think it would be better to stay in the US while your application processes. I know being apart sucks, but if you're crossing back and forth constantly, CBSA is going to realize something is up and send you into the office to ask you a bunch of questions. The more you cross, the more likely you are to get a border agent that is going to be a stickler for the rules and get cranky that you're actually living in Canada as a visitor (which is technically a no-no). I don't exactly know if they'd do anything about it (like deny you entry) since you arent working illegally in Canada, but that many trips back and forth will certainly send up red flags. Every time you reenter Canada it's assessed as a new entry, so technically your 6 month stay starts over, but that's not always how they enforce it. I was told multiple times by CBSA as I crossed back into Canada (similar situation, American living with Canadian spouse in Vancouver, except I cross to visit family sporadically, not every day) that it's 6 months out of a calendar year, and told I should get a visitor record (allowing me to stay longer than the 6 months). Again, that's not the letter of the law, but it seems to be how they choose to enforce it.
If you apply under the In-Canada class (inland) and apply for an open work permit, you're covered by implied status, meaning you can stay in Canada beyond that initial 6 months should that time run out until a decision is made on the work permit, but the sponsorship/PR application itself does not mean you can stay in Canada. You have to maintain legal status in Canada as either a visitor, student, or worker for the duration of processing of an inland application, otherwise they can cancel it and you'll have to reapply. If you're going back and forth daily, that's more chances for them to deny you entry at the border, thus voiding your inland application. It doesnt happen often as far as I know, but it's something to be aware of. You can apply under the outside of Canada class (outland), you wont be able to apply for a work permit, but you also don't have to maintain status in Canada for it to be processed, so on the off chance you get turned around at the border trying to reenter Canada, your application won't be cancelled. Also, at least for US citizens, outland applications seem to be processing faster than inland ones as of right now. I can't tell you which to choose, there are pros and cons for both sides
It's not legal for you to fully move to Canada yet. If you were to show up at the border claiming to be moving in with your husband, with all your earthly possessions in the back of your car, without a Confirmation of Permanent Residence (what you get when your PR is approved), they will likely turn you right back around. It's perfectly okay for you to state that you're coming to stay with your husband for 6 months and apply for PR while you're there, as long as you look like a legitimate visitor. Again, I don't know how the transiting back and forth for work would change any of that, hopefully someone can give you better insight. I would guess that most of us who have come for a long term visit while waiting for PR have left previous jobs (my husband is my sole support right now while I wait).
As far as your application itself, there's only a cohabitation time requirement for common-law applicants. If you arent living together when you apply (if you choose to stay in the US) there's a separate list of proof of your relationship you'll need to provide (I think it has to do with proof that you've visited, chat/text message transcripts, etc.) If you do choose to live with him as a visitor in Canada, you need to prove that, but you don't have to show that you've lived there for a certain amount of time. For spouses, they are trying to assess the legitimacy of your relationship, and they know it's possible to have a legitimate marriage (as in you're not just in it to love to Canada) without living together.
I hope that covers most of your concerns. I'm not a lawyer or an immigration consultant, I've just done a ton of research and been on this forum a while (and I'm going through this process myself) so I'm just passing along the information I've found, feel free to take it with a grain of salt. I'm sure I've probably gotten something a bit wrong and someone will correct me
