First of all, what you want to be looking for is a wealth management / private banking / advisory firm or individual catering to High Net Worth Individual (HNWI) which is the linguo in the industry to describe individuals a fair amount of money, although the specific range varies. This article from the Financial Post suggests range of 1-5M USD, which is appropriate here. Above this, the term used is Very High Net Worth Individuals (VHNWI).
Rankings and reputation
One good starting point is to get a feel for who are the reputable wealth management advisors. Such lists abound (e.g. Forbes, CNBC, etc) and you should be able to find some firms in an area convenient for you. Ideally, you should refine your criteria to match firms delivering the type of services that you are looking for.
Both money and the service industry tend to be very personal. Nothing quite beats a referral from a trusted person. If someone you trust has made use of such services, you may ask them about their experience and whether they have some recommendations.
Choose your advisor
Even within a given firm, you can choose your advisor. Meet them, discuss with them, look them up on LinkedIn, try to find track records or reviews on their performance and service. If you like a firm but not the proposed advisor, ask to meet someone else.
At this level, the key differentiating factor between firms is often on the breadth and comprehensiveness of their services. Do ask about the full breadth of services they offer and then compare against different firms.