G'day John,

There's no quality difference between the two, it's just down to the strength provided.  A marquee spring will be a lot stiffer/stronger than the standard springs, as the gazebo style shelters have a great wind catch.
Go with the standard springs for any kind of camping tent, you'll get the best performance for your set up.

G'day Sarah,

You'll need to untie the knot on your existing guy rope near the plastic tensioner/slider and loop that around one end of the trace spring, then re-tie that rope end to the plastic slider. That should then be connected and you can peg your trace spring in.

G'day Dianna,

The loop will fit, yes.  The tracer spring won't be completely upright though, so as long as your guy ropes are pegged out a reasonable distance from your gazebo, and the pegs are put in at an outward angle, you'll be fine.