After doing some reading about “ancient greek railways”, hard stone roads with grooves for car wheels. I got to thinking, instead of a canal across the neck, could the north build an ice road? A trench of packed ice that would allow goods on sleds to be SLID from coast to frozen coast. or White Harbor to Winterfell. What do you think? Maintained with ice from farther north during spring it could stay frozen into summer until regular transport resumes