We crossed over at the Ambassador in early October. As others have mentioned, the construction is complete. We have a 40ft DP and tow an HHR so are close to 60 feet in length. When we have crossed before (many times)but we have been directed to the right hand side to use the truck facilities.
On the day we crossed last month, they were not busy and we were directed by the attendant to regular vehicle area and the "RV" lane there. This lane is located on the right hand side of and immediately adjacent to their new building. We proceeded through only to find that they have recently added a permanent building/canopy to the secondary inspection area just past the primary inspection booth. Since there is likely less than 6" clearance on either side going through the booth, a hard right hand turn to avoid the building must be made once the RV has passed the booth to avoid it particularly if you are in the first lane designated for RVs. Next you must head for a toll booth and get aligned to avoid the formidable curbs protecting the toll lane. Not an easy task. The Border agent could not understand why the RV lane was not relocated and recognized the difficulty reaching the toll booths when exiting.
Fortunately, it was not busy however I had to proceed slowly to access the toll lanes that took cash (on the extreme right) and in the process obstructed other traffic who were patient and appeared to understand my predicament.
I suggest you check the satellite views in Google Maps which have a fairly recent picture of the facility showing the canopy. It is easy to visualize the distance you have as you can see several nearby tractor trailers for length reference. You can also place the street view icon on the blue line past the booths to see it precisely.
Bob