The disadvantage of cantis is also their advantage: there are a number of variables that can be manipulated in the set up. This makes them fiddly for some to set up. But it also means that they can be adjusted to get a fine tune.

Everything else being equal, canti brakes stop as powerfully as anything other than high-quality disc brakes.

And, while I cannot make out the model of the bike, I can see that it is a Lotus touring bike, and as such is worth putting effort into.

So, I would do the following:

-true up the wheels so that you can bring the pads right up against the rims. This is especially important for cantis, since they have such a short pull levers in the first place.

-clean up the braking surface and get some new pads.

-Bring that yoke down. Most any LBS will have a bunch of old yoke cables around of different lengths.

-Check the routing and condition of the cables and housing.

With a little work you will have a pretty damn cool old touring bike with brakes that could stop a rhino.

jim