1. Do I being the sponsor, have to land in Toronto POE the same time as my spouse or can I fly in a week later?
You don't have to accompany your wife when she lands. If she is asked, she says you are tying up loose ends and will arrive a week later.
2. I am still trying to find a job in Canada but might end up coming back to US after 3-4 weeks of staying in
Canada since I am not sure if I will get employed there. I still have a job in US and with wife being pregnant and expecting in June, with no baby delivery coverage(unless get third party coverage) since we are planning on landing in end of March, I might have her deliver the baby in US. I understand process gets lengthy for baby becoming canadian, which i dont mind. We cant land by Dec 2012 but if we land after baby is born we have to apply for the newborn which is a lengthy process. I
Whats your opinion on this?
Since you are Canadian and pass on citizenship to your children, it is not a big deal if the baby is born in Canada or not. Sure it is a lengthy process to get the citizenship card for the baby but you do not have to stay in the US and wait for this. If you apply through the Canadian embassy, you can apply for a temporary Canadian passport for the baby so it can travel. Another option would be to get the baby a US passport for travel and bring it with you to Canada on visitor status and apply for the citizenship card from the inside.
3. We plan on landing for a week , driving to detroit for a wedding for 4 days and returning through land border by car and then staying in toronto for 2-3 weeks, with plans on flying back from Toronto after a couple of weeks back to US for her to "Accompany" me in US if i dont find anyjob that quick in Toronto. I would be lucky and hopeful if i did. Please give your suggestion on the timings and situation.
I don't see a problem.
4. Since I am a returning resident (currently Canadian and US citizen with non-residency) status, is there a possibility I will be questioned upon my return to canada, for example did you quit your job in US, do you have any job interviews in Canada, etc by the Immigration officer?
I much doubt it. As a dual citizen, you are allowed to live in either country. As a citizen sponsor of a spouse from overseas, I assume you had to show plans to move to Canada when she would get her PR. If anything, she might be asked about that when she lands but you are not coming until a week later. If you are asked, you can say that you are coming to look for jobs while you may still keep your job in the US for a while until you find one in Canada.