strategy of looking for external reviewers in grant applications Some grant applications require aplicants to find external reviewers. First, we can't look for co-authors. Who else can we look for? Friends? Faculty who ever worked in the same school? Do the external reviewers need to be the immediate same field? People who don't know us at all? May I ask immediate associates to recommend their associates who don't know me at all?
For external grants that ask you to suggest reviewers (common in UKRI grants for example), you are expected to suggest someone who has the technical, theoretical, or methodological expertise to evaluate the proposal and who would have no conflicts of interest in doing so. In other words, no one that you have an active research project with, no one who you have had significant past research collaboration with, no one that you go down to the pub with as friends, and likely no one in your institution. You can and should suggest people that you know to be collegiate and who are generally friendly to your work, that's expected. The granting body will then consider your suggestions and will likely select one or two of those you suggest mixed in with someone you don't suggest just to balance things out. It is unwise to try to game this any further than suggesting someone who you know generally likes what you do as reviewers are asked to disclose any conflict of interest. For them to reveal there is a conflict that you did not reveal does not sit well.

For an internal grant, that will likely be a bit different and it is best if you get clarity from your institution as to what they expect. They may expect reviewers to be internal.