How to use coveo in place of lucene in existing application
I have an existing search page, which is using default lucene in sitecore ecommerce application. There are sort dropdown and pagination as well. I want to replace these two with coveo's provided components.
Please suggest how should i proceed for the same.
I think the answer to this question contains the answer you are looking for.
As Jeff mentionned, you have to replace your existing search components by Coveo ones, that is not only the sort dropdown and pagination, but the result list and searchbox as well since Coveo does not use LINQ.
In his answer, Jeff shared a link to the Coveo for Sitecore Hive documentation. This framework contains all the relevant Coveo components that you need (sort components and paging components) to use for this task. I would suggest going through the getting started tutorial. This should help you understand how the framework works.
You start by doing what I suggested on your previous question: https://answers.coveo.com/questions/14068/how-to-use-coveo-cloud-index-for-existing-sitecore.html
Pagination is out of the box with Coveo. There is a Coveo Pager component you can add to your Coveo for Sitecore Hive search page.