Good Morning, 

Thanks for your question. 

If you plan to leave the cardboard in place to smother the weeds before you do your planting, there are better ways to do this. 

Please click on the following link: https://extension.umn.edu/planting-and-growing-guides/solarization-occultation

Here is a link about quackgrass: https://extension.umn.edu/weeds/quackgrass

You did not indicate where the additional soil is coming from, but that may also contain more weed seeds to deal with. 

Depending on how closely you plant your native plants, you could add wood chip mulch to the entire area and plant your plant plugs in little holes you make in the wood chip mulch to keep the weeds down.  

Of couse there may be additional weed seeds that blow in and set seed in your area, so you will need to do some weeding until your native plants take over the area. 

Here is a link to a local author's website about pollinators and native plants for pollinators: https://www.pollinatorsnativeplants.com/softlandings.html

Thank you for taking care of the pollinators!

Good Luck!