I work in finance. It's not just your current salary if you've only been with this employer within recent months. For a mortgage, you will be required to provide substantial proof of income. For a car loan or something to that effect, a recent paystub is usually fine, unless you've just gotten that new job, in which case, they could request a copy of your T4 from the previous year.
Another factor that is considered with your current length of employment is how long you were with your previous job. Someone who goes from job to job every few months is a higher lending risk.
I often pre-qualify doing a quick assessment of a customer's TDSR (total debt service ratio, the magic 40% mentionned above). The actual process takes more time.
Current salary is ok if you've been with your employer for a substantial amount of time. (usually 2 years) Less than that, you should expect to provide more info.