I've locked through the Ballard locks from the Seattle Shipping canal into and out of the Puget sound many times single handed in my 22. In those locks there are two different styles (neither of which is similar to the Sault Ste. Marie locks). In the small locks out here, there are cleats on the wall that float up and down with the rising/lowering water. For those you wrap your lines around the floating "button" and tie back off to the boat. You have to make sure that you can rapidly provide line in the rare event that one of the floating buttons sticks as long as you pay attention and didn't tie off too firm or with a gazillion unnecessary wraps around your cleat, it's pretty easy to provide additional line.
In our "big locks", there's a fixed cleat at the top and the lockmasters attach your bow and stern lines to the fixed cleats. Then as the boat rises or falls, you have to feed or take up line manually. Typically this is done by wrapping around (but not tying off) a bow and stern cleat and standing in the cockpit to tend the lines. For large boats, you may need a person on each line as it can take some strength to keep the lines fairly tight. For a small boat without much draft (like a C-Dory) it's pretty easy.
As I understand the Sault Ste. Marie locks, there are fixed vertical cables at fairly regular spacing (maybe 2' apart?) that you can use to loop a line around. As these cables are fixed at the top and bottom but have no attachment to the wall in between, the lines simply slide or roll up the cable as you lock through. Correct?
In such a case, I'd still use two lines one from the midships cleat (just outside of the helm window) and one from the stern. The reason for using two lines is that you always want to release the line that is down current first (and tie it last). If you instead release the up current line first, that end of the boat can rapidly swing around the pivot point provided by the down current line and it can be hard to recover from that - especially if it is the bow swinging around.
My single handed procedure for locking through always had a line at the midships cleat. Prior to entering, I would fender both sides of the boat. This would allow me to lock to either side and, if needed, raft another boat on my side. In our locks, we are often rafted several deep so LARGE fenders are good as you may need a lot of fender depending on the shape of the boat you raft to or that rafts to you. I would come in and:
1) if moving into current, tie the boat off from the midships cleat while it was still in motion and then put the boat in gear to hold it against the wall while I dealt with the stern line. OR
2) If moving with the current, put the boat in neutral and tie off the stern line prior to typing off the boat line. Either way, the motion of the boat keeps the boat against the wall.
3) Then (with sufficiently long lines), I would do one wrap around the boat cleats and stand in the cockpit with one in each hand to keep the lines taught while going up or down. Unless you have one or more larger boats rafted to you, it's easy to handle. If you have other boats rafted to you and you anticipate a strong current, ask one of the people on that rafted boat to step onto yours to help tend the lines. Make sure you give them detailed and firm instruction since you never know whether they are newbies or experts (or idiots). Also, if you are rafted to a bunch of boats, be prepared to start your engine if needed to keep the group perpendicular to the wall. I've had to do that when the line tenders on the inside were either not paying attention or were not strong enough to keep boats rafted 5 deep in place.
4) When leaving, release the down current line first and put it in the cockpit. Then release the up current line and motor slowly off the wall.
Key items:
Large fenders - more than you think you might need.
Fairly long lines - you want to make sure that they are long enough to go from your boat's cleats to the wall and back such that you have both in your hands in the cockpit.
A handy knife in the rare event something hangs up and you need to cut a line prior to it ripping out a cleat or turning your boat over.
Patience - a swear some divorces must get their starts in the locks out here.
Situational awareness and a willingness to spring into action to help others, fend off boats who don't know what they are doing apply power if needed etc. If you're rafted and someone near the wall is losing control, don't feel bad about jumping onto their boat to offer help. It is often appreciated, especially by older cruisers who can afford very large boats but may not have the strength necessary for some locking procedures.