Google will automatically pickup the reviews from other sites but you can increase the speed of sync by making sure your profile is an exact match on the review sites. It is highly recommended that you take over the ownership of your profile on each of the top local review sites and optimize your business information. We have tested this technique and it worked well.
Here are the details of the test.
Sample -
Business A - New Google Place account and exact matching Judysbook.com + Citysearch account (exact headline, address, and tel#).
Business B - New Google Place account and Judysbook.com + Citysearch account with a different headline but same phone number and address.
Business C - New Google place account and JJudysbook.com + Citysearch account account with different phone # but same address and headline.
Business D - New Google place account and Judysbook.com + Citysearch account account with different address but same headline and phone #.
Submit each Judysbook.com + Citysearch account landing page to Twitter and digg manually one time only after reviews have been added. (Spam free Twitter account with 2000+ followers and clean Digg account with 50+ followers and regular diggs)
Outcome
Google picked up the reviews from Judysbook.com for A and Citysearch account for B.
Note - Google only picked up 1 or 2 reviews for both A and B from the review site so there could be some special algorithm in place for selecting the reviews based on quality.
I will be writing a blog post on my blog on this study soon.
Hope this helps.
Sameer