ProQuest Ebook Central links can be found by clicking on "Share Link to Book" on the left side, underneath the "Read Online" and "Download Book" buttons.
The link can be shared as it is; it does not need Langara's proxy prefix added.
You can also link directly to a particular page. When you are in the Read Online view, click on the chain link icon in the menu at the top:
Copy the link in the "Share This Book" pop-up window. It will bring you back to the current page.