Advice on career switch

For the M&A, your career prospects will depend on whether your company is the acquirer or acquiree. If it's the latter, unless your work performance is outstanding, otherwise, current supervisor(s) may not have much say in your career progression.

Usually though not immediately, an organisation re-structuring will take place whereby the acquirer starts promoting their own staff to head many of the merged divisions/departments. Next, one could see fellow colleagues one by one being "washed overboard" (starting with those deemed high-pay staff). This may sound absurd but that's how businesses streamline to stay afloat. In the M&A, the acquirer is only interested in the assets that the acquiree has to offer.

Anyway, the eventual decision lies with you... goes with your heart/head.

After Merger, i think likely will start to retrench to save cost.

Go for the higher salary.

Make the jump since there is opportunity ahead! Yearly increment is quite difficult to get higher salary~