I have been down there but have no great experience with either region.
I based my belief on two things. The Canadian border is larger (and has more mountains/geographical challenges) and I know some Border Patrol veterans who now live here in Washington. They say the geography here would be (and is) more difficult than it was in California, Arizona, and Texas where they worked.
There are great challenges to fencing either border but I disagree with those who say it cannot be done. I don't think it would be 100% effective but if we stopped most of the traffic with Mexico it would pay for itself IMO.
The reality is that neither party is willing to address the issue.
It's not only the terrain, there's also heat, rattlesnakes, scorpions etc., to contend with and armed criminals living in slums within feet of the border.
What we should have done was build a replica of the Panama Canal on the southern border and made the peanut farmer come up with the funds for it.
The issue is being addressed and the construction is underway as we speak in several areas by the NG.