If the white stuff can easily be scraped off and is dry underneath, I guess it is powdery mildew, the worst case I have ever seen. It spreads in cool humid weather without rain. It is not usually a big problem in PA.

If it is PM, hose it off with a strong spray and apply a fungicide such as Safer's sulfur or potassium bicarbonate (various brands). But I would consider discarding this variety of rose.

Or at least move it.

You're growing hostas successfully there, which implies rather shady conditions. Roses prefer a lot more sun than hostas do (even though the bright blooms would look good against those variegated leaves, the rose bushed really need better air circulation and more sunlight.)

The holes and some of the white marks on your leaves could be from rose slugs.

As Michaelg stated see if some of that white stuff wipes off... That would be powdery mildew...

ROSE SLUGS are little worms found on the underside of the leaves...

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Also, on watering: roses like less frequent, deeper watering, not frequent, shallow watering. Are you watering from the top of the plant, or around the soil? I prefer watering during the day, so that any water on the leaves can dry quickly. Leaving water to sit on the leaves overnight can encourage fungal diseases like powdery mildew and blackspot.

I planted a new Thomas Affleck rose in May and I notice its getting some powdery mildew on it. Actually first rose I ever seen with PM here...

Definitely more than one thing going on here. For PM you can get a fungicide spray. It will keep it from getting worse but the leaves already with it on them will not clear up. You'll need to wash those off. Just use a good hard spray of water and that will also help to dislodge the rose slugs that are putting holes in the leaves. Make sure to spray up under the leaves to get the back sides where the slugs are.