I had a similiar problem where the bottom plate of my 1st floor met the sill. There were 'sporadic' gaps between the 2 but mostly only big enough for spiders and crickets to get through. I used a low-volume expansion foam to 'fill' the gaps. You could probably use the high pressure foam but check w/your builder for his recommendation. Since I don't think he's misleading you, his recommendation as to which foam to use (IF you're doing it yourself) should be fine.
Since you can see daylight, it sounds like you have the same problem I did. My best to ya and hope this helps.