Have you tried restaurants that have play areas for kids? I don't know any that are in your part of the world but we've found a three in inner NE. Two of those have seating right next to the open kids' area, or at least did a few years ago. When we arrived during slow hours we could watch and even interact with my granddaughter at the same time we were eating.
I've also eaten at a couple of quieter places where I could go where my granddaughter could stay in her stroller. My idea for why this worked is that she was used to being in her stroller, eating from the tray, playing with her toys that were attached to the stroller.
If your toddler will stay seated in the high chair and only whines I'd try completely ignoring the whining. Give him something to do but if he knocks it off the table still ignore him. If his whining escalates pick him up, take him to a quiet place, calm him but don't play with him. Go back to the table and keep repeating this until he understands that he'll be taken away from the action if he acts out. Or try taking him to the car, put him in his car seat which will keep him confined. Ignore him as much as possible so that he learns that crying and screaming doesn't get him what he wants. Soothe him on the way out by talking calmly about why you're doing this, etc.
I've not tried or seen this done but I've read about doing this sort of thing and the success that the parents have had. I also don't remember the age of the toddler or if it was a preschooler.
My daughter and I still pick up carry out so that her kids can still be active away from us but still visible (when they were younger) and we could eat and talk at the table. It doesn't have the social stimulation that a restaurant gives us but we still get to eat the good food that we haven't prepared and don't have to wash dishes. Several of the more upscale, ie; not take out per se, now have a parking spot right by the door or even a drive thru for take out orders.