On the assumption your measurements are in mm, not cm (300 cm is 3 metres and no container would be that wide), that would make your pot (in feet and inches) about two and a half feet deep by roughly a foot across, or 80 cm deep by 30 cm wide. The tree you've mentioned will grow in it for a while, but inevitably, over time, its growth will be very much constrained by the lack of root space, so although its impossible to say what height and spread it might reach, its safe to say it definitely won't reach 3m in height. After a while, it may start to look rather sick - most large plants are okay in largeish pots for up to 3, possibly 4 years, but after that, they start to look 'thin' and weak.

Any plant that can be expected to reach 3m won't do so in a pot, I'm afraid. Since your intention is to create something that blocks the view from a window above, have you considered some kind of small pergola, single or double row, with a pot either end of the size (but preferably larger) you mention, with perhaps a climbing plant in each, which, if the pergola is only 6 feet tall and a foot or two across at the top, might mean you could get some of the growth across the top? That would block the upstairs view of the area beneath, even though its not high enough to block their window. Or a shade sail similar to this https://www.primrose.co.uk/sail-shades-c-85.html which would have the same effect, though the effectiveness of these alternate solutions rather depends whether the neighbour's window is opposite your home, to the side, or directly above you.