Leon, thanks for the update. I have another concern, how long can continue to travel via US. I am not sure when the PR will renewed. If it takes more than six months what is the alternative. It is with CSU section now.
There is no time limit on how long or how often you can enter via the US but you can prepare for a little hassle each time. However, they will probably get to know you if you cross often and always do it in the same place.