What tall shrubs can I plant that will offer a backdrop for perennials?
This will depend on your area, and climate zone. What is your USDA zone?
Are the scare the cat plants, annuals or perennials?
"Scare the cat plant", or Plectranthus caninus, is a perennial in areas where it's hardy (zones 10 and higher), but it only lives for a few years, so it's considered a short-lived perennial.
Just had a big area cleaned of old branches,fallen trees, would like to put something on ground,but do not want to mow. Is there something we can cover the ground with ? It is wet and fairly sunny.
I will need your USDA zone to recommend plants that are suited for your area, but in the meantime, this article will get you started in the right direction: https://www.gardeningknowhow.com/ornamental/water-plants/wgen/water-tolerant-plants.htm
I have an area in my yard that gets all day sunshine. Here in Northern Arkansas temps reach 90 degrees and above for several weeks. Everything I plant burns up and dies. Please recommend a perennial or shrub that can withstand the heat and sun.
These sites will give you some ideas for heat- and sun-tolerant plants:
http://extension.psu.edu/plants/gardening/eco-friendly/heat-drought-tolerant-plants
https://www.gardeningknowhow.com/ornamental/flowers/fgen/full-sun-plants.htm
http://www.johnson.k-state.edu/lawn-garden/agent-articles/trees-shrubs/shrubs-for-summer-color.html
There are also some bulbs and groundcovers that will do well:
https://www.gardeningknowhow.com/special/xeriscape/drought-tolerant-ground-covers.htm
https://www.gardeningknowhow.com/ornamental/bulbs/bgen/bulbs-for-hot-climates.htm
These articles may also help with heat-protection strategies:
https://www.gardeningknowhow.com/plant-problems/environmental/heat-stress-plants.htm
https://www.gardeningknowhow.com/plant-problems/environmental/dealing-with-heat-stress.htm
How can I arrange these in a perennial border: pennisetum foxtrot, kniphofia flamenco, & salvia windwalker?
You pretty much have your choice, as long as you do not block light from the other plants. I would talk to a local landscaper in your area, as they will be able to tell you if your arrangement works for the area that you are trying to plant in, and if there is anything that needs to be done to your soil.
What kind of tree that does not get very tall? Maybe 10 to 12 feet at the most.
There are very many. This will depend on your climate zone, whether this will be indoors or out, your experience level with small trees, and a few other factors. Can you provide me with as much information as possible? I will be more than glad to suggest something for you.
where can i buy flowers that grow in shade in Toronto?
We can't recommend specific retailers. But, you can look over the following articles about flowers for shady spots, then head to any gardening store or to online retailers to look for seeds or plants:
https://www.gardeningknowhow.com/special/shade/shade-tolerant-flowers.htm
https://www.gardeningknowhow.com/special/shade/finding-a-shade-loving-plant.htm
https://www.gardeningknowhow.com/ornamental/flowers/impatiens/growing-impatiens-flowers.htm