Q2  The city had my yard sprayed for weeds (2018)

1. I cannot comment on whether your yard has weeds or not, not having seen it.

2. What I suggest is: become familiar with the weed bylaw(s) of your municipalitiy. Many have exceptions for native wildflower or perennials. Work wit the municipality at updating it if needed. (doesn't work well to be adversarial)

3. Commercial products can only be applied by a licenced applicator. I believe the application of restricted products requires more training. see legislation/Saskatchewan or look up the Pest Control Products Act and Regulations of your province. If the municipality hired an applicator without a license (provincial), or if the product is not used according to label (federal PMRA inspector), you have recourse under the law. There is a glitch in the regulations though. I believe they still require only the supervisor be licensed and not the 'underlings'. Be aware that you will need a lot of persistence and money to go to court and win anything, and the cases I know of cost more than they brought back. You will usually be charged with the bill for the cleaning and spraying. An appeal may be able to prevent that if there were irregularities.

4. People usually only give me a product name. Check the pesticide's ingredients and designation (commercial, restricted, domestic) at pesticide labels. Be aware that most pesticide formulants (called inerts in the USA) are still secret and there are still many toxins used. We mostly dont know what formulant is used in what product.

5. Courts are for redress of measurable things, mostly monetary compensation. They have done very poorly on health issues or even contamination issues. 

6. All I know about remediation, and it isn't much. Pesticide persistence is measured in half-life, the time it takes for 1/2 the dose to be broken down. The same amount of time would be required to break down 1/2 of that to 1/4 and the same to break down 1/4 to 1/8 of the original application, etc. This time can vary with soil type, moisture and other conditions. Breakdown products can be more persistent. Currently, soil sterilants ( 3-5 years) and the insecticide neonicotinoids (imidacloprid: 40-124 days in soil) are the most persistent, as well as glyphosate (2- 197 days average 47 d). While the halflife of pyrethrins is relatively short in soils, they persist a long time in sediments or indoors where the breadkdown mechanisms don't exist or are slowed down. If the half-life of a pesticide is relatively short, you may not need to remediate. It will disappear in time, hopefully. Dicamba which is part of most lawn herbicide formulations has a half life of 30-60 days. Try googling half life for active ingredients of concern.

7. if you expect an apology from the city/municipality, give it up. It will likely never happen.

8. You may be able to have the soil in you yard replaced or topped with new topsoil but, really, you don't know where that comes from and whether it was sprayed or not, or whether it ill be full of weed seeds. Up to you.