Yes, if that other company is a member of Multiple Listing Service (MLS) - which most real estate companies are. For Sale By Owner (FSBO) properties are not listed in MLS so a Sales Representative likely would not be able to provide information regarding them. However, with a Buyer Representation Agreement, your Sales Representative may be able to help you purchase a FSBO.
The sale of the severed portion of vacant land would not be subject to GST/HST since it is not capital property used primarily (more than 50%) in a business and it is not being sold in the course of a business. However, if the land was subdivided into more than two parts, sales of the severed portions are not exempt unless the portion is sold to a relative (or to a former spouse or common-law partner) for their personal use.