Putting Photo-Paint art in CorelDraw

I have a few years of experience with CorelDraw and I'm still learning how to do things, I actually have CorelDraw X7 Home & Student. I am helping design wedding invitations for my brother's wedding. I'm making a range of drafts for him and his finace to choose from, one idea has a water coloured rainbow that looks painted. Thing is I've only used Photo-Paint for doing bitmap editing using the effects and all. I need to know how to use Photo-Paint to make a rainbow using the paintbrushes and then putting that rainbow in CorelDraw so I can put it on the front of the folded invitation. The invitation is 7.2 x 9.2 open faced portrait orientation, as it will be folded like a clam shell. To add to the rainbow, I'd like to add clouds too. I thank you to whoever can help teach me.

Thank you in advance for taking the time to help me.