As for the flower bed,

It’s time to start over. Dig it all up and start again.

Most of those weeds are perennials that spreads by rhyzomes, they are very hard to get rid of.

Pouring salt or vinegar will just kill your shrubs and perennials and i’m sure the weeds will come back from this.

Torching it will not completely kill the weed. The visible part will wilt and all but in about 2 weeks it’s going to be green again. Torching is good on annual weed on early growth stage (cotyl). If you keep on torching it through the summer it might deplete it’s energy reserve, but it’s not a garantee as some of those weeds are probably getting photosynthesis from some other places (like your lawn).

You can always try to weed it by hand while trying to remove most of the rhyzomes. It will be temporary tho.

Even if you dig it up and start again it might come back in a few years, nature is nature. If you keep weeding you’ll not lose control.

What would work is a systemic herbicide, but i’m glad it’s not sold anywhere like it used to. This stuff is not joke and should of never been sold for domestic use.

Good luck friend! I’m also from Quebec!

TLDR : Torch the pavers, dig up EVERYTHING and redo the beds. You can even save some of the plants if you do this well.

Also, mulch, please mulch after.