Is that a 27” rim there now? That would mean the canti’s pivot and design (brake pad contact) is right at the limit (by appearances) for the 27” rim (630mm diameter). The 700C rim is 622mm in diameter or 4mm shorter radius at the brake pads.
If you want to use the 700C rims, this suggests you would need to lower the pivots if possible, get offset brake pad holders if available, or find new canti brake calipers set up for a 700C reach with the current pivots you have.
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Italvega and Torpado Enthusiast