Insert Effect

The easiest way to do this is to just insert the effect in the FX bin of the track (or an FX Chain in the ProChannel, and then use an automation envelope to turn the effect on during the required bars. You'll have to read up on how to draw automation to do this. But it's the most versatile way of triggering effects on specific bars. 

KPerry
Or add to the clip's own FX bin.

Good idea but one drawback - any tails (especially with Delay) will be chopped off once the Now time reaches the end point of the clip.
 
I would go with the solution offered by mettelus - clone the track, isolate the clip(s) you want the effect added to and delete the rest.
Now you put your Delay effect in the Track Fx bin with no worries about tails.
 
Remember to mute (or delete) the corresponding clip(s) in the main track

I borrowed an idea from a live setup.  I wanted to use a fader on my control surface to control the feed as opposed to using a mouse.... I want to mix in real time as mix as possible... and clean it up after - the same way you might with midi.
 
In this session in particular - I Created 2 busses in sonar - 1 is title delay feed - the other is titled Delay.   The delay buss had an eq - comp - delay - de esser - delay - and a post fader send to the main verb.  in that order -
 
I sent lead vocals, Lead guitar to the Delay Feed - as - in this particular track - they both would benefit from this.  Now - I could use a longer throw fader to be more expressive with my delay feeds - catching just a word... or sneaking up the delay on long notes... or long words... and feeling like I wesnt just being clinical in using a mouse.
 
I also found that I could be more musical - even if I automated the delay feed with a mouse in real time - it has a much larger and easier to understand footprint than a rotary encoder.
 
So now I've automated my delay feeds coming in - I can easily control the return volume and eq in its own bus