To link to the app, you can use this URL form:
itms-apps://itunes.apple.com/app/id{APP_ID}
It uses the itms-apps protocol to link directly to an app on the App Store and avoid redirects.
If you want to link directly to the review page, it appears that the only way is to use a URL in this form:
itms-apps://itunes.apple.com/WebObjects/MZStore.woa/wa/viewContentsUserReviews?id={APP_ID}&pageNumber=0&sortOrdering=2&type=Purple+Software&mt=8
Example
The bit about type=Purple+Software
is literal (not the name of your company); it appears to be a codename for iOS apps.
The {APP_ID}
for your application can be found in two places on iTunes Connect (even before you release your application or submit it for review).
The first is in the URL of the application in the "My Apps" section, which is in the form
https://itunesconnect.apple.com/WebObjects/iTunesConnect.woa/ra/ng/app/{APP_ID}
You can also find it on that page in the "General App Information" section right under your App Icon:
