Hi
This is a classic market place SaaS (Software as a Service) and the classic answer for getting both sides is quality content, quality marketing, and word of mouth (which you'll get once you provide quality service).
The key issue, BEFORE you think about how to get them to your platform is to first create a POC (proof of concept) to make sure that people want to use such a marketplace - doing this is fairly easy and will save you hundreds of hours, and tens of thousands of $ building the website.
I've helped numerous startups working on marketplaces and would be happy to advise you on doing the POC (and connecting you to a development company if you want one). I can also help you create the basic landing pages for the POC.
Good luck
I've successfully helped over 350 entrepreneurs, startups and businesses, and I would be happy to help you. After scheduling a call, please send me some background information so that I can prepare in advance - thus giving you maximum value for your money. Take a look at the great reviews I’ve received: https://clarity.fm/assafben-david

If i understood correctly. you want to provide a top quality service by someone with a deep experience in the field but at a price affordable to a small/medium sized business. Unfortunately, I think this is not easy to do unless you play on volumes. To hire such people you need to pay them 'a lot', snatch them from other existing opportunities, ask them to provide their knowledge for a return which may not be suitable to them. It seems rather difficult idea to me, personally. However it can be discussed more. Let me know if interested.
P.S: I am new to this platform but old with the skills.

Hello:
Yes, your idea is relatively easy to understand, but execution will indeed be challenging.
On the consultant side, what can you offer outside of lucrative engagements? Have you built this business around a purpose? Are there intangibles that will not only attract top talent but retain it?
On the client side, what does your marketplace offer that no other does? If you address a well-identified niche, you are more likely to become essential to these clients. Also, how are you structuring your offerings? Are they accessible to all types of clients?
Please let me know if you’d like to discuss further.
Cheers,
Kerby

I've worked with about every major consulting firm in the last 5 years (I work for a large publicly traded company that has gone through mergers, re-organizations, etc.)

Interesting concept - like fivver on an upscale market? In my experience CEOs don't typically browse the internet to hire high quality consultants. They read an article or see a speaker that speaks to an issue their business has and then starts a relationship with that person that will then lead to a possible consulting engagement. When companies hire consultants they are seeking a solution that is tailored to their situation or company. I don't know if they will start buying in a more on-line less interactive mode or not moving forward; but I would spend some time on how companies buy what you are trying to sell.

As far as getting top consultants - many are paid 25% of an engagement they sell and another 25% of the engagement they deliver (workshop, speech, assessment, etc.). That is what you are competing against + their company provides research, copy, content, editors, etc. So they would lose that too since they could hardly go on their own while also working for a Bain or McKinsey.