Yes, both of these are potential issues.
(First, you are entering by land, so the ESTA is a non-issue. ESTA is for air/sea entry only.)
I will presume that you will be entering without a visa, under the visa waiver programme.
In this case, the I-94W form requires an address in the USA. I do not believe that "UNKNOWN" is accepted, but I may be wrong. If you can obtain a reservation somewhere for your first night and write that in, it's a good start.
Second, the suggestion that you won't know how much time you will spend within the USA is not helpful for a CBP agent. His job is to assume that you are going to break immigration law and overstay. Your job is to satisfy him that you will not.
If you can prove that you will definitely leave in one month (or less) then that is fine. Usually this could be accomplished by proof of residency and firm connections in Vancouver, or by onward travel out of Canada already booked within a month, or by some other tangible document.