For "Proof of Work Experience" CIC have mentioned to provide work-related details in a single letter. I already have such letter from my previous employer with all the details mentioned there except the annual salary and benefits. But I do have a separate letter for salary details from that employer (Promotion Letter with Salary Details).
Can I show the two letters side-by-side for that purpose or should I include everything in a single letter?
Perfectly legit to showcase multiple letters. While uploading in the post ITA application, you'll have to combine those mutliple docs into a single PDF document and also provide an optional cover note explaining the purposes of each of the documents.